1. Field of the Invention
This invention in general relates to calculators and more particularly to a calculator designed to solve part load problems for air conditioning or refrigeration systems.
2. Prior Art
The selection of a refrigeration system has heretofore been principally made by ascertaining the design load of a building or other device to be conditioned or refrigerated and by matching equipment to that load. The awareness of energy costs has pushed the equipment selector to look for high efficiency equipment under these conditions.
However, it is apparent that most air conditioning equipment does not operate at full design load for more than a minimal period each year. Most of the year operation is under part load conditions wherein the unit is oversized such that some method must be accomplished of producing less than the full unit capability. In addition to simply cycling a unit between on and off typical ways of reducing capacity of the system are cycling the compressors, using compressor cylinder unloaders, and using hot gas bypass. This combination of load limiting devices act to effect the efficiency and performance of the system.
As it becomes more apparent that the energy efficiency and power consumption of a system should not be determined solely at design temperature then part load efficiencies at which the unit is typically operated must also be evaluated. It then becomes necessary to find some method of calculating this part load performance. Heretofore the use of a computer having an emperical data base has been utilized for making these part load calculations. However, the use of the computer brings the inherent disadvantages of accessing the computer, programming and the turn around time period.
The subject matter herein concerns a hand held slide rule type calculator operable to quickly calculate part load performance such that energy consumption and efficiency of the unit can be calculated at various design and off design conditions.
By the use of this calculator it is possible to quickly and in the field ascertain the energy consumption of the unit under operating conditions other than design conditions. It is also possible to determine the capacity of the unit at that part load condition. The calculator, as presented, considers eight variables. These variables are building design load, building partial load, unit or system nominal capacity, unit or system partial capacity, unit or system nominal power, unit or system part load time based average power consumption, design ambient and part load ambient temperature. Entering condenser water temperature may be utilized where appropriate in lieu of the ambient air temperature. This calculator may be used to solve for any one of the unknown variables knowing the other seven. In a typical application of this calculator four of the variables are known and the others are selected to ascertain operation under part load conditions.